Large craniomaxillofacial (CMF) injuries significantly impact a patient's quality of life, compromising the ability of the skull to protect the brain and he patient's ability to speak and eat. Craniofacial bones also give the face its shape and structure; therefore, craniofacial bone defects negatively impact the individual's psychosocial well-being. Approximately one million fractures requiring bone transplantation occur annually in the US, with more than 200000 of these being in the CMF region. These incur an annual economic burden in excess of $3 billion [Desai, 2007]. The current gold standard for repair - autologous bone grafting of the free fibular flap [Brydone et al., 2011] - results in significant donor-site morbidty and is limited by the amount of useful bone that can be harvested. Hence, there remains a huge need for alternative grafts. Other options include metal and polymer prostheses, which are not ideal due to the inability of metal and polymer to integrate well with native bone [Park et al., 2001]. Tissue engineering seeks to overcome these limitations by generating biologically active grafts comprising cells, scaffolds, and bioactive factors. In the CMF region in particular, the scaffolds can be designed to meet the mechanical, cosmetic, and biological demands of the functional tissues. Naturally-derived scaffolds promote bone formation due to the presence of embedded biomolecules [Urist, 1965; Sampath et al., 1981; Harakas, 1984]; however, obtaining clinically relevant volumes of decellularized bone for scaffold production is difficult and the process labor-intensive, leading to high procedural variability. Thus, while naturally-derived scaffolds feature superior biological properties, their manufacturing is challenging. On the other hand, 3D printing is a newer technology that builds a structure layer-by-layer as opposed to carving a shape from a bulk stock. This approach greatly increases the types of geometries that can be made and has been explored in the construction of bone engineering scaffolds [Eshraghi and Das, 2010; Park et al., 2012]. Synthetic scaffolds can be produced in high quantities, in tightly controlled processes, and with patient-specific geometries, but incorporating bioactivity into them is difficult. The objective of this proposal is to combine the advantages of both synthetic and naturally-derived scaffolds by developing a hybrid scaffold composed of bone extracellular matrix (ECM) particles embedded in a larger polymer phase, in which the overall biomimetic properties of the scaffold derive from the bioactivity of the bone and from the controllable geometry of the polymer by virtue of 3D printing. This undertaking will be achieved within three Specific Aims: 1. Find the optimal size and maximum concentration of bone particles to incorporate into the polymer. 2. Evaluate the effect of partial demineralization on te bioactivity of hybrid scaffolds. 3. Use the optimized hybrid scaffolds to repair a critically-size murine calvarial defect.